The present disclosure relates to an optical scanning device using a multi-beam light source and an image forming apparatus using this.
A laser printer, a copier and the like include an optical scanning device for forming an electrostatic latent image on the circumferential surface (surface to be scanned) of a photoconductive drum by scanning and exposing the circumferential surface with a laser beam. The optical scanning device includes a BD (Beam Detect) sensor on which a part of the laser beam is incident to synchronize a write start timing on the photoconductive drum. Normally, a laser light source for emitting the laser beam is mounted on a circuit board (APC board) mounted with an APC (Auto Power Control) circuit, and the BD sensor is mounted on a circuit board different from the APC board.
A single-beam optical scanning device is known in which a laser light source and a BD sensor are mounted on the same circuit board. According to this device, the number of sensors used can be reduced and a drive circuit can be shared by the both.
Further, a multi-beam optical scanning device is known in which a multi-beam laser light source and a BD sensor are mounted on the same circuit board. In a multi-beam system, a dot pitch in a sub scanning direction on a photoconductive drum needs to be adjusted according to a set resolution (dpi) of an image. This adjustment is performed by slightly rotating the laser light source about an optical axis. However, in the case of mounting the laser light source and the BD sensor on the same circuit board, a problem arises in which the position of the BD sensor changes according to the rotation about the optical axis and a laser beam is not incident on a light receiving surface of the BD sensor. In this device, using an optical element (anamorphic lens) for converting a spot of a detection beam propagating toward the BD sensor into a spot long in the sub scanning direction, the detection beam can be detected by the BD sensor even if the position of the BD sensor is shifted due to the rotation.
However, according to the technique of the above device, a special optical element for forming a detection laser beam to be incident on the BD sensor is separately necessary. This leads to an increase in the number of components and a cost increase. On the other hand, in the case of mounting the laser light source and the BD sensor on the same circuit board without using any special optical element as described above, how to adjust the rotation of the laser light source about the optical axis and fix the laser light source on the circuit board thereafter becomes problematic.
An object of the present disclosure is to provide a multi-beam optical scanning device capable of precisely fixing a circuit board while adopting a configuration for mounting a light source and a sensor for synchronizing a write time on the same circuit board, and an image forming apparatus using this.